Prasutagus was king of a British Celtic tribe called the Iceni, who inhabited roughly what is now Norfolk, in the 1st century AD. He is best known as the husband of Boudica.

Prasutagus may have been one of the eleven kings who surrendered to Claudius following the Roman conquest in 43, or he may have been installed as king following the defeat of a rebellion of the Iceni in 47. In any case, as an ally of Rome his tribe were allowed to remain nominally independent, and to ensure this Prasutagus named the Roman emperor as co-heir to his kingdom, along with his two daughters. Tacitus says he lived a long and prosperous life, but when he died, the Romans ignored his will and took over, depriving the nobles of their lands and plundering the kingdom. Boudica was flogged and their daughters raped. Roman financiers called in their loans. All this led to the revolt of the Iceni, under the leadership of Boudica, in 60 or 61.

Coins have been found in Suffolk inscribed SVB ESVPRASTO ESICO FECIT, "under Esuprastus Esico made (this)" in Latin. Some archaeologists believe that Esuprastus was the true name of the king Tacitus calls Prasutagus, while others think he was a different person. Others interpret Esuprastus is a compound name, with "Esu-" deriving from the godEsus and meaning "lord", "master" or "honour", and "Prasto-" being an abbreviated personal name, the coin inscription thus meaning "under Lord Prasto-". It is also notable that coins of the Corieltauvi have been found inscribed with the similar names IISVPRASV and ESVPASV. The name of an earlier king of the Iceni appears on coins as SCAVO, a name which may be related to the Latin scaeva, "left", and scaevola, "left-handed". Both rulers' coins are similarly Roman in style and language and were probably issued within twenty years of each other. Chris Rudd suggests that Esuprastus, whom he identifies with Prasutagus, succeeded Scavo after the Icenian rebellion of 47.